What Is The Smallest Casement/Vertical Window Air Conditioner

As the summer season draws closer, many people are scrambling to find the best air conditioner to deal with the hot, sweaty conditions. The good news is that there are endless products to choose from, especially when shopping for a central AC, mini-split, or portable air conditioner.

Problems begin when you set out to find the right window air conditioner. Although you have just as many options to pick from, finding the right window AC for your application can be a daunting task. It gets even worse for vertical windows. Matching your window to the right air conditioner can be a hell of a challenge.

The following are six great options when shopping for a vertical window air conditioner. We’ve taken into account vital considerations, including capacity (in BTU), efficiency rating (in EER), noise rating (in decibels), and price.

What are Vertical Window Air Conditioners?

There are multiple ways to categorize windows. One approach is categorization by dimensions. In this approach, the conventional window wider than it is tall, is known as a horizontal window. Meanwhile, windows that are taller than they are wide are known as vertical windows.

Vertical sliding windows are an excellent example of vertical windows. Another configuration popular with the vertical design is single-hung windows. If your home has any of these two window types, one or both are likely vertical models.

Vertical window air conditioners are everyday window conditioners customized for use in vertical window configurations.

They are characteristically narrow AC units that are taller than they are wide. While standard window air conditioners for double-hung windows are broad and short, the typical vertical window air conditioner is narrow and tall.

Make sure to measure the target window before you head out shopping. You need a minimum window width of 15 ½ inches. You’ll also need a special vertical installation kit. Fortunately, most manufacturers include the necessary kit in the package.

The two best vertical window air conditioners are the 10,000 BTU Model FFRS1022R1 from Frigidaire and the 8,000 BTU Model CAC8000W from Koldfront.

Casement vs Vertical vs Sliding vs Horizontal Window Air Conditioners

Unfortunately, there is no standard term for narrow window air conditioners. You can call it a sliding window AC, slider window AC, casement window AC, or vertical window AC. The terms are often used interchangeably and may refer to the same thing.

However, to avoid confusion, especially when ordering the product online, it’s best to use more formal terms. The following are the formal names for the different window air conditioners;

  • Sliding window ACs: Sliding window ACs are air conditioners that fit sliding windows. The air conditioners are designed such that you can slide the window as close to the AC as possible and use the kit to fill any remaining gaps.
  • Slider window ACs: A slider window ACs are practically the same thing as sliding window air conditioners. The two terms are used interchangeably.
  • Casement window ACs: This term refers to window air conditioners that fit casement windows, the type of windows that open fully without a centerpiece as in doubly hung windows.
  • Vertical window ACs: Are air conditioners explicitly designed for narrow, vertical windows, often single-hung and vertical sliding models.

Advantages of Vertical Window Air Conditioners 

The truth is that you can use most other window air conditioner types in vertical windows without any issues. For instance, a sliding window air conditioner will effortlessly fit a vertical sliding window without much fuss.

However, it’s always better to bring in a vertical window air conditioner for your narrow windows for a few reasons, including;

  • They are a better fit: The average horizontal window air AC may not necessarily fit a vertical, narrow window. Often, the height is too short. If you’re not prepared to compromise on AC performance, a vertical model would be your best option.
  • The kit fits better: This is another significant advantage of choosing vertical ACs for vertical windows. The vertical window is much better suited to vertical window AC kits. It’s even easier to fill in any remaining spaces between the kit and window.
  • Better for aesthetics: Even where a horizontal style AC would do the job, a vertical window looks better with a vertical window air conditioner. It’s a much more proportional fit and gives your home a more balanced outlook.

What Size Window AC do you Need? Discussing Physical Dimensions

This is a major factor when choosing a window air conditioner, vertical or otherwise. You must pick the right size or risk various consequences.

Standard window air conditioners require that the window is at least 20-inches wide (width), though some can work with windows up to 25 inches wide. For vertical windows, the required width is smaller. Most models are designed for windows narrower than 20 inches. It’s why nearly all narrow window air conditioners are no wider than 15 inches.  

That’s not the only thing you need to consider, though. For one, the installation kit will take some space on the window too. On average, installation kits add an inch to the window AC’s overall width, though some can be larger.

Manufacturers don’t include the additional width when providing window AC dimensions. It’s your job to keep the kit in mind.

Another important consideration is height. Even though vertical windows have enough space height-wise to accommodate most vertical ACs, you still want to make sure that you’re getting a good match for your window.

Sizing a Vertical Window Air Conditioner; Discussing BTUs

The capacity of the air conditioner is another critical consideration. You must find the correct size for your room as under and overcooling are bad for your health and your house’s health.

Undercooling would leave you feeling warmer than necessary, negative the purpose of cooling in the first place. An AC that’s too small for the job may also run unnecessarily longer and at the highest possible speeds. Overworking the AC can result in faster wear and tear and more frequent repairs and replacements.

On the other hand, an air conditioner too big for the application tends to cycle more frequently to maintain the thermostat setting. Too frequent ON-OFF cycles can damage the internal components of the air conditioner. It’s also a waste of money bringing in extra BTUs that you don’t need.

In general, you need 20 BTUs for every square foot, equating to about 7,000 BTUs for the average 350 square-foot room and 8,000 BTUs for 400 square feet. Add 400 BTU for kitchens and adjust the value upwards by 10% per foot for higher ceilings.

Other Factors to Consider when Purchasing a Small Vertical Window Air Conditioner

We’ve already mentioned the need to consider capacity in BTU and physical dimensions (width and height) of both the window and the AC. Four other important factors are;

  • Efficiency: The efficiency of a window air conditioner is measured in EER, though SEER is also common. Aim for 11+ EER and 16+ SEER where applicable.
  • Noise rating: Window air conditioners tend to be noisy. But, you still want to find the least noisy option you can find. Anything below 58 decibels is considered good enough.  
  • Convenience features: Convenience features include remote control, smart features, timers, sleep mode, energy-saver mode, and self-diagnostics. 
  • Warranty: The best window air conditioners have a reliable manufacturer warranty. You want 4+ years on the sealed system.

Vertical Window AC FAQs

How do you install a window air conditioner in a vertical window? It’s the same as installing any window AC. You need to purchase Plexiglas and cut out a hole in it for AC venting. Then, install the Plexiglas on your window and caulk or weather-strip the area around the vent for airtightness.  

Can I make a vertical window AC out of a regular one? No. To convert a vertical AC into a standard unit would require placing it on its side. It’s strictly prohibited to place any AC on its side as it would compromise the unit’s functioning. 

Why are there so few options in vertical window ACs? Because double-hung windows are still the most popular and these models work better with horizontal window air conditioners. Also, consumers generally prefer standard air conditioners for whatever reasons. 

How Long Can You Leave A Window Air Conditioner Running? It’s completely safe and even recommended to run the AC round the clock throughout the cooling season. Although the power bill will be high, it’s better to be safe than sorry. Keeping the AC on round the clock keeps you healthy and safe. 

Can a vertical AC be installed in a wall? Yes. However, the wall installation process requires a different, specially-designed sleeve. Never attempt to install the AC through the wall with the window installation kit. 

Smallest Casement Window Air Conditioners

1. Frigidaire FFRS0822S1 8000 BTU Heavy-Duty Slider Casement Window AC

The model FFRS0822S1 air conditioner by Frigidaire is a product you’ll come across quite often when shopping for a casement/sliding window air conditioner, and a good reason. It’s exceptionally effective both performance and style-wise. Better still, it’s reasonably priced (compared to similar options) and very efficient. 

Designed for medium-sized applications, up to 350 square feet, the 8,000 BTU air conditioner is a 10.8 EER appliance that guarantees at least $66 in cost savings yearly. You can save even more with the low-speed modes/settings.

The Sleep Mode particularly stands out. It provides sufficient cooling at very low noise levels while consuming low power. You also have the option of an Energy-Saver mode that consumes even less energy. 

The other operational modes include Fan-Only and Cool Mode. In the fan-only mode, the fan circulates, alone or alongside the AC function, for a cool, relaxing environment.

Better still, the appliance doubles as a humidifier function to remove excess moisture from the room at 3.0 pints/hour. A built-in thermostat maintains your ideal room temperature and is controllable from the onboard control panel or LED digital remote.  

It’s a 740-watt appliance that plugs into the standard household power outlet and best fits 21.5-inch to 40-inch windows (height) by 15.5-inch windows. A 6.5-foot cord is included for effortless installation. 


  • Powerful performance up to 263 CFM
  • 4-way air directional control 
  • Three fan speeds and several operating modes
  • Washable filters, with filter reminder 
  • 1-year parts, 4-year sealed system warranty


  • No auto-restart function 
  • No smart/Wi-Fi control

2. Koldfront CAC8000W 8,000-Watt BTU 115V Casement Air Conditioner

Another excellent alternative for casement window air conditioning is the Koldfront model CAC8000W. It’s also an 8,000-BTU air conditioner designed for the standard 120V 15A household power outlet. An included NEMA 5-15P standard-size plug makes the connection effortless.

The Energy Star-certified air conditioner is compact enough to fit windows from 15 ½ and 16 ¼ inches wide and at least 20 5/16 inches high and supports remote control from up to 16 feet away. 

It’s an extremely energy-efficient air conditioner, rated 11.1 EER and fairly quiet too at 53 dB at the maximum speed level. The lower speed levels are as quiet as 51 decibels. You get to choose from three different fan speeds – 177 CFM, 206 CFM, and 235CFM. 

You’ll also appreciate the multiple operating modes, including the Cool mode, Energy-Saver mode, Fan-Only mode, and Dry mode. An additional pre-setting, the Sleep mode, enables quiet, convenient night operation. Whichever the setting or operating mode you choose, the washable air filters guarantee a clean and healthy indoors by eliminating any foreign particles from inbound air. 

The package includes all installation hardware and weather seals and targets rooms up to 450 square feet. We also love the long 72-inch electrical cord. This appliance comes with a 2-year manufacturer warranty for your peace of mind. 


  • Powerful 8,000 BTU cooling
  • Extremely efficient at 11.1 EER
  • Doubles as pints/day dehumidifier
  • Includes all installation hardware 


  • No smart/Wi-Fi controls

3. Arctic King AKSC08CR61 8,000 BTU Casement Air Conditioner

You may have noticed that the best small vertical window air conditioners are rated 8,000 BTU. This model from Arctic King is another one-ton solution to consider. For one, it is Energy Star certified, which is often enough endorsement for some shoppers.

It also functions as a dehumidifier, so you don’t need to spend an extra $100 on a moisture-removing appliance. The dehumidifier function removes moisture at 0.9 pints/hour, equivalent to 21.6 pints/day. 

It’s a 1.0PH air conditioner and plugs into the standard 115V power outlet, meaning you don’t need extra wiring. At 6.6 amps and 734 watts (cooling), it easily outperforms competing models in energy conservation. The included NEMA plug type 5-15P receptacle makes electrical connections effortless. 

The air conditioner easily fits windows between 15.5 inches and 16.3 inches (width) and at least 21.3 inches tall/high. It is designed for rooms up to 350 square feet. It features three fan speeds and pre-set operating modes for your convenience.

The modes that stand out include the auto mode, energy-saver mode, and sleep mode. An auto-restart function restarts the cooling at the previous setting in the vent of a power outage. 

Other features that stand out about the model AKSC08CR61 AC include the follow-me remote, filter check lights, and a 24-hour timer. An LED display on the unit shows the remaining time on your timer. You get a one-year warranty to protect the investment. 


  • Durable, weatherproofed build
  • Doubles as a dehumidifier and fan 
  • 4-way air direction control
  • Slide-out filter access 


  • Short, 1-year warranty

4. Frigidaire FFRS1022R1 10,000 BTU 115V Slider/Casement Window Air Conditioner

The final three products are 10,000 BTU air conditioners, and the first option is the ever-reliable Frigidaire model FFRS1022R1 designed for medium-sized rooms, up to 450 square feet. It’s a 323 CFM AC though you can choose lower operating speeds depending on your needs. It has three-speed settings. 

The 10.4 EER air conditioner is reasonably energy-efficient, and although it’s not Energy Star certified, it’s approved by both the Consortium for Energy Efficient (CEE) and UL listed.

The antimicrobial filters keep any foreign particles from entering the home via the AC, and there’s even a filter indicator to alert you when it’s time to change the filter. A built-in auto-shutoff feature offers protection by cutting the power supply in case of emergencies. 

There are many other features to like about the Frigidaire FFRS1022R1. It’s a 4-way air direction/circulation system that disperses air thoroughly throughout the room. Unfortunately, it’s a bit loud at about 61 decibels.

Control is via the onboard control panel or the included remote control device, though the various pre-set operating modes allow you to enjoy convenient air conditioning without doing much work. 

The AC works best for windows up to 15.5 inches wide and comes with an extra-long 3-prong 72-inch power cord and mounting hardware for quick installation. Remember that professional installation is still required. 


  • Ideal for up to 450 square feet 
  • Features built-in auto-shutoff 
  • Fitted with washable microbial filter
  • Mounting hardware included


  • Requires professional installation 
  • Short warranty (1-year)

5. PerfectAire 10,000 BTU Slider Casement Window Air Conditioner

The PerfectAire model 3PASC10000 is another thoughtful option when shopping for a 10,000 BTU casement window air conditioner.

Designed for spaces up to 450 square feet, it’s excellent for windows between 15 ½ and 16 ¼ inches wide and at least 21 ¼ inches high. It’s always advisable to physically measure your window dimensions before you head out shopping. 

An adjustable thermostat (built-in) keeps temperatures within the desired range, i.e., 62˚F to 86˚F, equivalent to 17˚C to 30˚C. However, you also have three-speed settings to choose from in both cool and fan modes. Three other operating modes, Cool, Dry, and Auto, allow you to pick the desired air conditioning level without bothering with the manual settings. 

Although a remote control device is provided for convenient control, you can always fall back to the onboard controls whenever you wish. All the settings are available from the control panel, including the Sleep mode, programmable timer, and louver adjustment function. The timer runs for 24 hours. Washable antimicrobial filters inside the AC help clean the air. A check filter reminder will alert you when it’s time to replace the filter. 

The air conditioner is rated 9.5 EER and 61 decibels, though the lower speed levels are quieter, at about 56 decibels. A 1-year manufacturer warranty backs it. 


  • Powerful 10,000 BTU cooling 
  • Three fan speeds, multiple operating modes
  • Full-function, follow-me remote control
  • Convenient front tilt-out air filter access 


  • The one-year warranty is short
  • No smartphone/app control

6. Global Industrial Casement Window Air Conditioner

Finally, the model MWDUL-10CRN1-BCJ4 AC from Global Industrial is a name that will always pop up whenever you mention heavy-duty casement window air conditioners.

It’s a 10,000 BTU air conditioner that employs 4-way air direction/circulation and can cool up to 450 square feet. Multiple fan speeds and operating modes allow you to configure the unit to deliver optimal cooling and general air conditioning. 

The 76.9-pound unit consumes about 1040 watts during cooling and can move as much as 550 cubic feet of air per minute (550 CFM), the highest on this list. However, lower speed levels are available, down to 450 CFM, for the not-so-hot days. 

A built-in thermostat keeps track of ambient temperatures and can automatically keep your home at the correct cooling levels alongside the various pre-set controls.

Alternatively, you can also adjust the control panel’s cooling conditions or via the provided remote control device. In the dry mode, the Ac turns into a humidifier to eliminate excess moisture from your home. The humidifier function can remove as much as 2.3 pints per hour. 

Though not the quietest, the AC operates at a modest 59 dB, which is acceptable for most consumers. This AC is best suited to windows between 15 ½ inches to 16 ¼ inches wide and at least 23.0 inches high. 


  • Features 24-hour timer and auto-restart
  • Full pre-assembled for easy installation
  • Includes 7.5-foot power cord 
  • UL and CUL listed, DEO certified 
  • 1-year parts, 5-year sealed system warranty


  • No smartphone/app control
  • Not Energy Star Certified 

Wrap Up

Although you many options to choose from when shopping for a window air conditioner, if it’s a vertical window, you’d be best off with a vertical window AC.

Vertical AC units fit vertical windows better and offer a better balance, which is important for your home. Above all, they are specially designed for the unique qualities of vertical windows.